The murder rate in the U.S. is projected to rise by about 13 percent for 2016, but almost half of that increase is due to violence in just one city, Chicago. There were 762 murders last year in America’s third largest city, a stunning 58 percent increase in homicides from 2015.

Theories abound as to why — from a slow down by the police, illegal guns streaming into the city, declining community-police relations and a lack of resources for disadvantaged neighborhoods.

Data compiled by the Denver Medical Center between 2000 and 2013 — during a period when death rates from gunshot wounds increased by about 6 percent every couple of years — suggested the increasing severity of gunshot wounds and the increasing number of patients shot multiple times, was making it more likely today than 10 years ago that shooting victims would die as a result of their wounds, reported The Denver Post.

More than a decade ago, when homicides were spiraling, researchers lauded the skill of hospital trauma units. In 2002, University of Massachusetts-Amherst sociologists published a study that found improvements in emergency medical services dramatically suppressed murder rates in the U.S. between 1960-99 even though overall violent assault rates rose dramatically.

The research found that the number of victims dying from criminal assault went down almost 70 percent from 1960-99, with annual declines of between 2.5 percent and 3 percent for firearm assaults, and 3.5 percent and 4 percent a year for other assaults.

The primary reasons for the dropping homicide rate, according to the study, included the development of 9-1-1 services, the rapid stabilization and transport of trauma victims by trained medical professionals, the nationwide proliferation of hospitals into non-urban areas and the development of specialized trauma units.

There were 4,331 shooting victims in Chicago last year, according to police records. A new study by the Journal JAMA Surgery found, between 2009 and 2013, almost one in five gun-related injuries that met the criteria for treatment at a trauma unit throughout Chicago’s Cook County were initially under-treated at non-trauma facilities.

“I was not surprised by the number of cases treated in hospitals without trauma units ... What did surprise me was the number of firearm injuries,” Lee Friedman, associate professor at the University of Illinois at Chicago, and a co-author of the study told CNN.

Among those with injuries that met the criteria for treatment in a trauma unit about 18 percent received initial treatment at a non-trauma facility, and only about 10 percent of those were transferred to a trauma facility.

One of the very things that the University of Massachusetts-Amherst study heralded as driving homicides down — treatment at trauma unit — is happening with less frequency in Chicago.

The Chicago study involved an analysis of nearly 10,000 gunshot injuries over five years, reported CNN. The criteria for a patient to be transported to a specialized trauma unit include the patient’s level of consciousness, vital signs and location of injury, for instance whether a gunshot wound is to the head, neck, torso or above the elbows or knees, according to the Center for Disease Control and Prevention.

In this era of increasing fire power and automatic weapons is it possible that one in five gunshot wound victims in Chicago don’t meet the criteria for treatment in a trauma hospital?

Last year was not the deadliest in Chicago’s history, nor is Chicago the most deadly city in America per capita. However, the fact that Chicago had more murders last year than the two largest cities in America, combined, calls for close scrutiny of every potential contributing factor to this dire situation.

If Chicago’s failure to timely and adequately treat gunshot victims is contributing to the rise in homicide, that problem can be fixed. Before policymakers send in the “feds” or the National Guard, maybe instead they should consider Doctors Without Borders or the Red Cross.

— Matthew T. Mangino is of counsel with Luxenberg, Garbett, Kelly & George P.C. His book “The Executioner’s Toll, 2010” was released by McFarland Publishing. You can reach him at www.mattmangino.com and follow him on Twitter @MatthewTMangino.